A fracture locus for a 2 wt% aluminum-graphene metal matrix composite at 300 °C

Deformation behavior of a 2 wt% aluminum-graphene metal matrix composite (MMC) at 300 °C is studied. The MMC under study is synthesized at the Institute of High-Temperature Electrochemistry, Ural Branch of RAS. Data on ultimate ductility of the MMC is obtained. The value of shear strain to fracture is used as the characteristic of ultimate ductility. The shear strain to fracture is the function of the stress triaxiality coefficient and the Lode-Nadai coefficient. Tensile tests of smooth cylindrical specimens, notched cylindrical specimens, tensile and compressive tests of bell-shaped specimens, and tests of thick-walled cups with thinned bottoms are used to study ultimate ductility. The fracture locus of the composite at 300 °C is identified by the results of the study. It has been determined that graphene increases the ductility of aluminum, even under conditions of prevailing tensile stresses. However, the influence of graphene is significantly dependent on the form of the stress state of the metal under deformation. The composite under conditions of tension of smooth cylindrical specimens manifests practically unlimited ductility. The specimens underwent plastic deformation till the moment of the physical separation of specimen parts in the fracture region, while the cross section of the specimen in the neck tended to zero. However, when thick-walled cups with thinned bottoms are tested, the influence of graphene on ductile properties of the MMC can be neglected. Under conditions of prevailing compressive stresses, the ductility of the MMC significantly increases for all the test types. The obtained fracture locus is compared with the fracture loci of commercially pure aluminum and the 1 wt% aluminum-graphene MMC. It has been determined that the ductility of the material increases with graphene content.